Communication apparatus, method of controlling communication apparatus, and non-transitory computer-readable storage medium

ABSTRACT

A communication apparatus operable to act as a master-AP in a multi-AP (access point) coordination configuration that supports an IEEE802.11 series standard, selects a sounding method which is a method for transmitting a sounding packet for receiving a CSI report as feedback from a terminal apparatus in accordance with a CSI (channel state information) calculation capability in the terminal apparatus that is connected to the communication apparatus.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wireless LAN communicationtechnology.

Description of the Related Art

An IEEE 802.11 series standard is known as a communication standardrelated to a wireless LAN (local area network). The IEEE 802.11axstandard uses OFDMA to achieve high peak throughput as well as improvecommunication speeds in congested situations. Note that OFDMA is anabbreviation for Orthogonal Frequency-Division Multiple Access.

After having been a SG (study group) called an IEEE 802.11 EHT (Extremeor Extremely High Throughput), an 802.11be TG (task group) is now activein a subsequent standard to the IEEE 802.11ax standard for furtherimproving throughput.

A multi-AP coordination configuration in which a plurality of APs(access points) coordinate and operate is being considered as one of themeasures for achieving the goal of this TG which is to improvethroughput. In order to operate this multi-AP coordination configurationefficiently, it is common to perform a sounding procedure between anaccess point (AP) and a terminal (STA). A sounding procedure is aprocedure for an STA to receive an NDP (Null Data Packet) as a “soundingpacket” from a plurality of APs and to transmit a feedback packet whichincludes channel state information (CSI) to each AP (Japanese PatentLaid-Open No. 2016-526856).

However, in a conventional sounding procedure, a procedure for aplurality of APs to cooperate and operate to transmit a sounding framehas not been made clear. Also, in the conventional technique, inrelation to time-related overhead of the sounding procedure and a heavyload on the STA, it has been proposed, mostly, to reduce the amount ofCSI information (reduce the amount of feedback) transmitted by the STA.However, reducing the amount of CSI information makes the estimation ofa wireless medium inaccurate, and especially, in the multi-APcoordination configuration, effects of that inaccuracy such asinefficiency in medium usage and slowdown in speed can be significant.

SUMMARY OF THE INVENTION

The present disclosure in consideration of the foregoing problemsprovides an efficient sounding procedure in a multi-AP coordinationconfiguration.

According to one aspect of the present invention, there is provided acommunication apparatus operable to act as a master-AP in a multi-AP(access point) coordination configuration that supports an IEEE802.11series standard, the apparatus comprises: a selection unit configured toselect a sounding method which is a method for transmitting a soundingpacket for receiving a CSI report as feedback from a terminal apparatusin accordance with a CSI (channel state information) calculationcapability in the terminal apparatus that is connected to thecommunication apparatus.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a system configuration in anembodiment.

FIG. 2 illustrates an example of a hardware configuration of an AP in anembodiment.

FIG. 3A illustrates an example of an AP functional configuration in anembodiment.

FIG. 3B illustrates an example of an STA functional configuration in anembodiment.

FIG. 4 is a flowchart of processing that is executed when a connectionwith an STA is started.

FIG. 5 is a flowchart of processing that is executed when data to betransmitted to an STA is generated.

FIG. 6 is a flowchart of processing for selecting a sounding method.

FIG. 7 illustrates a configuration of a MAC frame.

FIG. 8 indicates a configuration of a trigger frame (TF).

FIG. 9 illustrates a configuration of a CSI report field.

FIG. 10 indicate configurations of a MIMO control field.

FIG. 11 is a sequence diagram “from a connection between the AP and theSTA until a selection of the sounding method”.

FIG. 12 is a sequence diagram “in a case of simultaneous NDPtransmission (no BFRP TF)”.

FIG. 13 is a sequence diagram “in a case of simultaneous NDPtransmission (with BFRP TF).

FIG. 14 is a sequence diagram “in a case of sequential NDPtransmission”.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments will be described in detail with reference tothe attached drawings. Note, the following embodiments are not intendedto limit the scope of the claimed invention. Multiple features aredescribed in the embodiments, but limitation is not made to an inventionthat requires all such features, and multiple such features may becombined as appropriate. Furthermore, in the attached drawings, the samereference numerals are given to the same or similar configurations, andredundant description thereof is omitted.

[System Configuration]

FIG. 1 illustrates an example of a system configuration in thisembodiment.

An AP 102 and an AP 105 are access points comprising a function(multi-AP coordination function) that can achieve a multi-APcoordination configuration. A multi-AP coordination function is afunction for achieving higher-speed or more stable communication inrelation to a connected terminal than when there is one AP bycoordination with the other APs. Here, a stable state is a state of anarbitrary combination of a good signal-noise ratio, low interference,low latency, and low jitter, for example. Note that there are variousmethods in techniques for achieving such a stable state. For example, aJTX (Joint Transmission) that uses a D-MIMO (Distributed Multiple InputMultiple Output); null steering; coordinated OFDMA; and fractionalcoordinated OFDMA can be given. The AP 102 and the AP 105, in a casewhere they are not executing the multi-AP coordination function, manageonly a network of a BSS (Basic Service Set) 101 and a network of a BSS104, respectively.

The AP 102 and the AP 105 are connected by a network (backhaul) 100. Thenetwork 100 is a communication means for connecting a BSS (Basic ServiceSet) and another network to each other when an AP constructs a DS(Distributions System). The network 100 is achieved by wiredcommunication such as Ethernet (registered trademark) and telephone lineor wireless communication such as LTE (Long-Term Evolution) and WiMAX(Worldwide Interoperability for Microwave Access). Further, the network100 may be a wireless LAN conforming to the IEEE 802.11 series standard.In such a case, the network 100 may be the same or different from awireless channel that is used between an AP and an STA.

An STA 103 and an STA 106 are wireless LAN terminals. These STAs arecapable of data communication with a plurality of APs. Datacommunication includes communication in the above-described soundingprocedure. Specifically, reception of an NDPA (NDP Announcement) and anNDP, transmission of a frame including a CSI Report field, and receptionof an NFRP TF (NDP Feedback Report Poll Trigger Frame).

[Configuration of Communication Apparatuses (AP, STA)]

In FIG. 2 , an example of a hardware configuration of APs (AP 102, AP105) in the present embodiment is illustrated. An AP has, as an exampleof its hardware configuration, a storage unit 201, a control unit 202, afunctional unit 203, an input unit 204, an output unit 205, acommunication unit 206, and an antenna 207. The storage unit 201 isconfigured by a memory such as a ROM or a RAM, and stores variousinformation such as a program for performing various operations whichwill be described later, communication parameters for wirelesscommunication, and the like. Note that as the storage unit 201, astorage medium such as a floppy disk, a hard disk, an optical disk, amagneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatilememory card, a DVD, and the like may be used in addition to a memorysuch as a ROM or a RAM. The storage unit 201 may include a plurality ofmemories and the like.

The control unit 202 is configured by one or more processors such asCPUs and MPUs, an ASIC (application specific integrated circuit), a DSP(digital signal processor), an FPGA (field-programmable gate array), andthe like, for example. Here CPU is an acronym for Central ProcessingUnit and MPU is an acronym for Micro Processing Unit. The control unit202 controls the AP by executing a program that is stored in the storageunit 201. Note that a configuration may be taken such that the controlunit 202 controls the AP by a program and an OS (Operating System) thatare stored in the storage unit 201 cooperating. Also, a configurationmay be taken such that the control unit 202 is made up of a plurality ofprocessors such as a multi-core system and controls the AP. The controlunit 202 may control the functional unit 203 to execute a predeterminedprocess such as an AP function, imaging, printing, and projection. Thefunctional unit 203 is hardware for the AP to execute predeterminedprocessing.

The input unit 204 accepts various operations from a user. The outputunit 205 performs various kinds of outputs for the user. Here, an outputby the output unit 205 includes at least one of a display on a screen, asound output by a speaker, a vibration output, and the like. Note thatboth the input unit 204 and the output unit 205 may be implemented by asingle module, such as a touch panel.

The communication unit 206 performs control of wireless communicationconforming to the IEEE 802.11 series standard, control of wirelesscommunication conforming to Wi-Fi (registered trademark), and control ofIP (Internet Protocol) communication. Further, the communication unit206 controls the antenna 207 to transmit and receive wireless signalsfor wireless communication. The antenna 207 supports communication forthe multi-AP coordination configuration. For example, in the AP, aD-MIMO (Distributed Multiple Input Multiple Output) transmission for aJTX (Joint Transmission) is possible. There may be plural antennas 207,although only one is denoted for simplicity in the figure. Generally,the number of antennas 207 (elements) is a number according to thenumber of streams. Also, a frequency band that is supported by theantenna 207, in addition to 2.4 and 5 GHz bands, is a 6 GHz band that isscheduled to be introduced from 802.11ax.

Note that the STAs (STA 103, STA 106) also have the same hardwareconfiguration as the AP illustrated in FIG. 2 . In such a case, thecontrol unit 202 can execute predetermined processing such as an STAfunction by controlling the functional unit 203.

In FIG. 3A, an example of a functional configuration of the AP isillustrated. As an example of the functional configuration of the AP,the AP has a communication control unit 301, a CSI processing capabilitysetting unit 302, a storage management unit 303, a UI (user interface)control unit 304, a multi-AP configuration control unit 305, a soundingmethod decision unit 306, and a sounding processing unit 307. Thecommunication control unit 301 performs control for performingtransmission/reception of a wireless signal to and from another wirelessLAN apparatus (for example, another AP or STA) via the communicationunit 206. The communication control unit 301 executes wireless LANcommunication control such as reception of a wireless frame from anotherwireless LAN apparatus, frame generation, and frame transmission inaccordance with the IEEE 802.11 standard series. The CSI processingcapability setting unit 302 sets (the value of) the CSI processingcapability of the STA based on information that is exchanged with theSTA and the like. The storage management unit 303 performs storagecontrol/management that is related to the storage unit 201. The UIcontrol unit 304 delivers to each configuration element a control signalaccording to an input operation to the input unit 204 by the user (notshown). The multi-AP configuration control unit 305 executes a multi-APconfiguration function by selecting a multi-AP configuration method inaccordance with the presence of a peripheral AP, the capability of theperipheral AP, and a connection state between the peripheral AP and theSTA. The sounding method decision unit 306 decides whether to performsounding processing by either an explicit method or an implicit methodwhich will be described below. The sounding processing unit 307 performssounding processing in accordance with a method that is decided by thesounding method decision unit 306. In the present embodiment, soundingprocessing is performed based on the CSI processing capability of theSTA.

In FIG. 3B, an example of a functional configuration of the STA isillustrated. The STA, as an example of its functional configuration, hasa communication control unit 311, a UI control unit 312, a CSIprocessing capability decision unit 313, and a CSI calculation unit 314.The communication control unit 311 and the UI control unit 312 are thesame as the communication control unit 301 and the UI control unit 304.The CSI processing capability decision unit 313 decides the CSIprocessing capability of the STA itself. The CSI calculation unit 314performs CSI calculation processing.

[Processing Flow]

Next, a processing flow of the AP having the above configuration will bedescribed with reference to the figures. The processing indicated belowmay be started when a BSS is started or at a desired timing during BSSoperation by the AP.

<Connection Processing Between AP and STA>

FIG. 4 is a flowchart of processing that is executed when a connectionbetween the AP 102 and the STA 103 is started. In step S401, thecommunication control unit 301 of the AP 102, when connecting with theSTA 103, exchanges capability information and operation informationtherewith. This is achieved by exchanging a Management frame thatincludes an information element (IE). The information element has beennewly defined in response to the progress in IEEE802.11 standardization.For example, it is an HT Capability element in IEEE 802.11n, a VHTCapability element in IEEE 802.11ac, an HE Capabilities element in IEEE802.11ax, and an EHT Capabilities element in IEEE 802.11be. Note that HTis an acronym for High Throughput, VHT is an acronym for Very HighThroughput, HE is an acronym for High Efficiency, and EHT is an acronymfor Extremely High Throughput. Also, a Management frame is a MAC (MediumAccess Control) frame such as a Beacon, a Probe Request/Response, anAssociation Request/Response, and an Authentication Request/Response.The multi-AP coordination function is a function that is introduced bythe IEEE 802.11be standard. Accordingly, capability information that isrelated to the function is included in an EHT Capabilities element.

In FIG. 7 , a MAC frame configuration that is specified by theIEEE802.11 standard is indicated. In a MAC frame 700, various fields areincluded. In Frame Control 701, subfields 721 to 731 are included. Inthe information element (IE) of a Frame Body 710, subfields 741 to 747are included. In an Address1 703, an Address2 704, an Address3 705, anAddress 707, addresses such as a BSSID, a transmission source, and adestination are set in accordance with a MAC frame type (Type 722).Also, in the MAC frame 700, a Duration/ID 702, Sequence Control 706, QoSControl 708, and an FCS (Frame Check Sequence) 711 are included;however, detailed description will be omitted.

HT Control 709 is specified as follows by the IEEE 802.11ax standard.That is, when the left-most bit is 0, the HT Control 709 is for HT (IEEE802.11n); when the left-most 2 bits are 10, the HT Control 709 is forVHT (IEEE 802.11 ac); and when the left-most 2 bits are 11, the HTControl 709 is for HE (IEEE 802.11ax). Note that the definition of theHT Control 709 for EHT (IEEE 802.11be) is unspecified.

In the Frame Control 701, a Protocol Version 721 is a 2-bit number whichindicates a protocol version, and in a case of an IEEE 802.11 frame, is“0”. The Type 722 is a 2-bit number which indicates the type of theframe and indicates one of Management, Control, or Data. The Subtype 723is a 1-bit number which indicates the subtype of the frame and indicatesone of Management, Control, or Data. To DS 724 indicates that thedestination of the frame is a DS (Distribution System). Also, in theFrame Control 701, From DS 725, More Fragment 726, Retry 727, PowerManagement 728, More Data 729, Protected Frame 730, and +HTC 731 areincluded; however, detailed description will be omitted.

In the Frame Body 710, the subfields 741 to 747 are the configuration ofthe EHT Capabilities element for IEEE 802.11be. In an Element ID 741, avalue that is related to the EHT of IEEE 802.11be follows a value of theHE Capabilities element of IEEE 802.11ax and is 255. A Length 742 is thelength of an information element. In an Element ID Extension 743, an EHTCapabilities element that is related to capability information or an EHTOperation element that is related to operation information is defined.EHT MAC Capabilities Information 744, EHT PHY Capabilities Information745, a Supported EHT-MCS And NSS Set 746, and PPE (Physical layer PacketExtension) Thresholds 747 are the same configuration as in a case ofIEEE 802.11ax (the HE Capabilities element).

In the present embodiment, a subfield (CSI processing capabilitysubfield) that indicates a capability (CSI processing capability/CSIcalculation capability) for calculating the CSI by the STA in the EHTMAC Capabilities Information 744 is defined. The CSI processingcapability may be decided by the CSI processing capability decision unit313 in the STA. The first example that is related to the CSI processingcapability subfield is a 1-bit number that indicates whether the CSIprocessing capability is “high” or “low”. The second example that isrelated to the CSI processing capability subfield is a 1-bit number thatindicates whether it is “capable” or “not capable of responding withinan SIFS (Short Inter Frame Space) to a plurality of sounding packets”.The third example that is related to the CSI processing capabilitysubfield is a time conversion value that is calculated from an equationconsisting of “the number of transmission/reception antennas” and “thenumber of streams” of the AP and the STA and a “desired coefficient”. Insuch a case, the present invention is not limited to a 1-bit number.That is, it may be two or more values. The fourth example that isrelated to the CSI processing capability subfield is a value that is thesame as the expression format of the processing capability of the CPU.In such a case, the present invention is not limited to a 1-bit number.

Note that a means for notifying the CSI processing capability is notlimited to the above-described CSI processing capability subfield. Asanother example, a configuration may be taken so that the HECapabilities element is used instead of the EHT Capabilities element. Insuch a case, a capability expression value will be a 1-bit number. Thisrestriction of a 1-bit number is due to the fact that what is Reservedin the 48 bit HE Capabilities element of the IEEE 802.11 ax standard is1 bit.

Yet another example for notifying the CSI processing capability is amethod of newly defining an Action frame of the IEEE802.11 standard andthen using it. In such a case, the expression of the capability ofinformation to be notified can be a desired number of bits.

Returning to the description of FIG. 4 , in step S401, the communicationcontrol unit 301 of the AP 102 exchanges capability information and thelike with the STA 103, and then in step S402, the CSI processingcapability setting unit 302 of the AP 102 determines whether the CSIprocessing capability of the STA 103 is obtained. If the CSI processingcapability of the STA 103 is obtained (Yes in step S402), the processingproceeds to step S403. In step S403, the storage management unit 303sets to an STA management table a value that indicates the obtained CSIprocessing capability. Here, the STA management table is a region thatholds the capability information and the state of the STA that are to benecessary when the AP manages the BSS (Basic Service Set) and is presentwithin the storage unit 201. If the CSI processing capability of the STA103 is not obtained in step S402 (No in step S402), the processingproceeds to step S404. In step S404, the CSI processing capabilitysetting unit 302 of the AP 102 determines whether the MinTrigProcTime ofthe STA 103 is obtained. In a case where the MinTrigProcTime of the STA103 is obtained (Yes in step S404), the processing proceeds to stepS405. The determination in step S404 is intended to confirm that anindex to be in place of a value that indicates the CSI processingcapability itself is obtained.

Here, a value that is indicated by MinTrigProcTime will be described.This value corresponds to the value of a Trigger Frame MAC PaddingDuration of the HE MAC Capabilities Information of IEEE 802.11ax. Thissubfield is a 2-bit number, and 0/1/2 respectively correspond to 0(zero) μsec/8 μsec/16 μsec of MinTrigProcTime. Note that the nameMinTrigProcTime originates from “a minimum value of preparation time forperforming a transmission using an RU (Resource Unit) that is assignedby a Trigger Frame (TF)”.

In FIG. 8 , a configuration of a trigger frame (TF) is illustrated. Atrigger frame is a frame to be newly introduced from IEEE802.11ax and isa frame for indicating an activation timing necessary for a plurality ofSTAs (users) to simultaneously transmit a frame, and the AP wirelesschannel information for using the frame, and the like. In Trigger Frame800 of FIG. 8 , various fields are included. Frame Control 801 is acommon field in the IEEE802.11 series and in the present embodiment, avalue that indicates that the field is a trigger frame of IEEE 802.11axis entered. Common Info 805 indicates information that is common acrossthe plurality of STAs (terminals) which are the destinations of thistrigger frame and includes subfields 811 to 813. Per User Info 806indicates individual information that is related to the destination ofthis trigger frame. Padding 807 is something for providing a temporalpostponement to a group of STAs that received this trigger frame. The APdecides from the MinTrigProcTime of each STA the temporal postponement(that is, the length of the padding 807). Generally, the length (value)of the padding that corresponds to the maximum value of theMinTrigProcTime among the MinTrigProcTimes of a group of STAs to be thedestination of the trigger frame is used. Also, in the Trigger Frame800, a Duration 802, an RA (Receiver Address) 803, a TA (TransmitterAddress) 804, and a FCS (Frame Check Sequence) 808 are included;however, detailed description is omitted.

In the Common Info 805, a value (Trigger Type subfield value) that isindicated by a Trigger Type 811 and description that corresponds to thevalue are indicated in a table at the bottom of FIG. 8 . For example, ina case where the Trigger Type 811 is 7, the Trigger Type 811 indicatesan NFRP (NDP Feedback Report Poll) TF. Also, in the Common Info 805, aLength 812 and a Trigger Type Dependent 813 are included; however,detailed description is omitted.

Once again, returning to the description of FIG. 4 , in step S405, theCSI processing capability setting unit 302 of the AP 102 sets to thevalue of the CSI processing capability the value to which theMinTrigProcTime is multiplied by a predetermined coefficient, and thenthe processing proceeds to step S403. Note that, a configuration may betaken so as to subtract a predetermined constant in place of multiplying(multiplication) the MinTrigProcTime by a predetermined coefficient. Inany case, the MinTrigProcTime is handled as something whose CSIcapability is higher the smaller its value.

In step S404, in a case where MinTrigProcTime of the STA 103 is notobtained (No in step S404), the processing proceeds to step S406. Instep S406, the CSI processing capability setting unit 302 of the AP 102sets to a default value the value of the CSI processing capability. Forexample, this default value is a value that in a case of a 1-bit number,means “low” or “unable to respond within an SIFS to a plurality ofsounding packets”. As described above, the reason why the CSI processingcapability of the STA whose CSI processing capability is unknown isestimated to be low is for reliably executing irrespective of thecapability of the STA the processing to be necessary thereafter.

Note that in a case where the STA 103 does not notify the CSI processingcapability to the AP 102 in step S401, an inquiry for the CSI processingcapability may be made to the STA 103 from the AP 102 in step S402.

<Data Generation to STA>

FIG. 5 is a flowchart of processing that is executed when data to betransmitted to the STA 103 is generated in the AP 102. The data is datathat is addressed to the STA 103 from the STA 106, data that isaddressed to the STA 103 from an STA (not shown) within the BSS, datathat is addressed to the STA 103 from a terminal on the network 100,data that is addressed to the STA 103 from the AP 102, and the like.

In step S501, the communication control unit 301 of the AP 102determines whether to transmit the generated data by a multi-APcoordination configuration. In a case where data is transmitted by themulti-AP coordination configuration (Yes in step S501), the processingproceeds to step S502. In step S502, the multi-AP configuration controlunit 305 of the AP 102 executes the multi-AP coordination function withan AP in the vicinity. Next, in step S503, the AP 102, as a result ofthe execution of the multi-AP coordination function, determines whetherto operate as a Master-AP or a Slave-AP of the multi-AP coordinationconfiguration. Here, a Master-AP is an AP that manages the multi-APcoordination configuration, and a Slave-AP is an AP that operates underthe control of the Master-AP. In a case where the AP 102 operates as theMaster-AP (Yes in step S503), the processing proceeds to step S507. Theprocessing in step S507 will be described later using FIG. 6 . In a casewhere the AP 102 operates as the Slave-AP (No in step S503), theprocessing proceeds to step S506.

The case of No in step S503 in the present embodiment corresponds to acase where the AP 102 is the Slave-AP and the AP 105 is the Master-AP.In step S506, the communication control unit 301 of the AP 102 transmitsthe CSI processing capability of the STA 103 in relation to theMaster-AP (that is, the AP 105). In the following step S508, thesounding processing unit 307 of the AP 102 performs the soundingprocessing of the Slave-AP.

In step S501, in a case where data is not transmitted by the multi-APcoordination configuration, the processing proceeds to step S505, andthe AP 102 performs Single-AP transmission processing. Regarding thisSingle-AP transmission processing, there is no characteristic operationof the present invention; therefore, description will be omitted.

Note that in the present embodiment, a case where the AP 102 that hasperformed the connection processing with the STA 103 is the Master-AP isassumed; however, the AP 102 may execute a multi-AP coordinationconfiguration function in relation to the STA 106 that has performed theconnection processing with the Slave-AP (AP 105). In such a case, the AP102 will perform processing for receiving information to be transmittedby the processing in step S506 from the AP 105 following the processingin step S503.

<Selection of Sounding Method by Master-AP>

Next, processing in step S507 in FIG. 5 will be described with referenceto FIG. 6 . In step S601, the sounding method decision unit 306 of theAP 102 performs a selection of whether to perform the soundingprocessing by an explicit method or an implicit method. The selectioncan be performed based on the capability information that is exchangedto and from the STA 103, the input information for the input unit 204 bythe user, a predetermined setting, and the like.

Here, the explicit method and the implicit method will be described. Inthe explicit method, first, the AP (beamformer) transmits the NDP (NullData Packet) as a sounding packet. The STA (beamformee) that receivesthe NDP calculates the CSI from the NDP and then feeds back the CSI tothe AP. By this, the AP estimates a reception condition in the STA of apacket that it transmits.

In the implicit method, first, the STA transmits the NDP as a soundingpacket, and the AP that received the NDP estimates the situation of theSTA from the reception state of the packet. As described above, in theimplicit method, the STA only needs to transmit the NDP at an assignedtiming and the processing load in the STA is lesser in comparison to theexplicit method for not needing the processing for calculating the CSI.Accordingly, in a case where the implicit method is selected in stepS601 (No in step S601), the problem of an increase in the processingload in the STA does not occur. Therefore, description of the processingof the implicit method (step S607) will be omitted.

In a case where the explicit method is selected in step S601 (Yes instep S601), the processing proceeds to step S602. In step S602, thefollowing processing branches in accordance with the value of the CSIprocessing capability of the STA 103. Note that in a case where thevalue registered in the STA management table in the processing in stepS403 in FIG. 4 is a 1-bit number, the value is made to correspond to“high” or “low”. That is, in a case where the value of the CSIprocessing capability is indicated by two values which express the twolevels “high” and “low”, the processing branches to step S603 or S606.In a case where the resolution of the registered value is greater than 1bit, the value is made to correspond to “high”, “medium”, or “low”. Thatis, in a case where the value of the CSI calculation capability isindicated by three values which express the three levels “high”,“medium”, and “low”, the processing branches to step S603, step S604, orstep S606.

In a case where the CSI processing capability is “high”, the processingproceeds to step S603. In step S603, the AP 102 performs “simultaneousNDP transmission (No BFRP TF (BeamForming Report Poll Trigger Frame))processing”. In a case where the CSI processing capability is “medium”,the processing proceeds to step S604. In step S604, the AP 102 decidesthe length (time) of the padding in BFRP TF. This decision processing isprocessing in which the larger the CSI processing capability is inrelation to the CSI processing capability that is classified in the same“medium” level, the shorter the padding time for CSI. Next, in stepS605, the AP 102 performs “simultaneous NDP transmission (with BFRP TF)processing”. In a case where the CSI processing capability is “low”, theprocessing proceeds to step S606. In step S606, the AP 102 performs“sequential NDP transmission processing”. The details of the processingof steps S603, S605, and S606 will be described later using FIGS. 12 to14 , respectively. After the sounding processing (one of steps S603,S605, and S606), the data transmission processing is performed (stepS608).

<Calculation of CSI>

Next, a CSI report field in a CSI frame to be generated (calculated) andthen transmitted by the STA will be described with reference to FIG. 9 .FIG. 9 illustrates a configuration of a CSI report field. A CSI frame isan Action frame whose category is an HT or an Action No Ack frame in theIEEE802.11 standard, for example. This CSI frame is something fornotifying Channel State Information to a beamformer. Note that an Actionframe is a frame whose Type 722 holds a value 00 and whose Subtype 723holds a value 1101 in FIG. 7 .

In FIG. 9 , an SNR in receive chain 1 901 is an 8-bit number and is asignal-to-noise ratio (SN) of a receive chain of the STA that transmitsa CSI report. Here, a receive chain is an object that performs thenecessary signal processing that is related to the received data. Inthis signal processing, filtering, amplification, downconversion, andsampling are included. A CSI Matrix for carrier 902 is a matrix that isderived from a CHAN_MAT of an RXVECTOR. Here, the RXVECTOR is a set ofparameters that are related to the reception of a physical layer of an802.11 frame, and the CHAN_MAT is one of those parameters. By thisCHAN_MAT, whether that frame includes CSI matrices or beamformingfeedback matrices is indicated. Note that, FIG. 9 is a configuration ofthe CSI report field in a case where the operation frequency band is 20MHz; however, in a case where the operation frequency band is 40 MHz,the CSI Matrix for carrier 902 is “from −58 to −2” and “from 2 to 58”.Further, Nb, Nc, and Nr in FIG. 9 are values that are assigned by theMIMO control field. Here, the MIMO control field is used for exchangingchannel state information or for managing the transmission ofbeamforming feedback information.

A configuration 10 a and a configuration 10 b in FIG. 10 arerespectively configurations of a MIMO control field before IEEE 802.11axand of IEEE 802.11ax. Note that, the MIMO control field of IEEE 802.11axis assumed to be used also in IEEE 802.11be. Here, the Nb is a numberdefined by a Coefficient Size field 1003 of the MIMO control field. TheNc is a number of columns in the CSI Matrix defined by an Nc Index field1001 of the MIMO control field. The Nr is a number of rows in the CSIMatrix defined by an Nr Index field 1002 of the MIMO control field.

Incidentally, a plurality of APs simultaneously transmitting a soundingpacket (NDP) by the multi-AP coordination configuration, for thereceiving side, corresponds to an increase in antennas of thetransmitting side. Here, the computation amount of CSI matricesincreases in accordance with the number of transmission antennas;therefore, in the simultaneous NDP transmission, the computation amountof CSI matrices increases in comparison to a method in which each NDP issequentially transmitted. Accordingly, in a case of executing asimultaneous NDP transmission method, in order to perform CSI reportfeedback that is related to an NDP within the SIFS time, the processingcapability per unit of time in the STA must be higher than theprocessing capability per unit of time that is related to the sequentialmethod.

Considering this point, in the present embodiment, as in the branch instep S602 in FIG. 6 , the AP 102 changes the sounding processing inaccordance with the processing capability of the STA 103. By this, theCSI report feedback that is related to all NDPs is caused to becompleted in a period based on a predetermined time (for example, SIFS).

<Sequence Diagram>

Next, the operation sequence of the AP 102 and the STA 103 will bedescribed with reference to FIGS. 11 to 14 . FIG. 11 is a sequencediagram “from a connection between the AP and the STA until a selectionof the sounding method”. In F1101, connection processing is performedbetween the AP 102 and the STA 103 (step S401). This connectionprocessing corresponds to the exchange of a Management frame such as aProbe Request/Response, an Association Request/Response, and anAuthentication Request/Response frame. In F1102, the AP 102 confirmswhether the CSI processing capability of the STA 103 is obtained (stepS402). In F1103, the AP 102 decides the CSI processing capability of theSTA 103. In this processing, a calculation of the CSI processingcapability from the MinTrigProcTime, a request for the CSI processingcapability in a case where it has not been obtained, a setting of theCSI processing capability to a default value, and the like are included(step S404 to S406). In F1104, the AP 102 registers the CSI processingcapability in the STA management table (step S403). In F1105, the AP 102recognizes that data addressed to the STA 103 is generated. In F1106,the AP 102 determines whether to construct the multi-AP coordinationconfiguration and then transmit data (step S501). In F1107, the multi-APcoordination function is executed between the AP 102 and the AP 105 andthe multi-AP coordination configuration is constructed (step S502). Inthe present example, it is assumed that the AP 102 is the Master-AP. InF1108, the AP 102 starts an operation as the Master-AP. In F1109, the AP105 starts an operation as the Slave-AP. In F1110, the AP 102 that isthe Master-AP performs a determination for selecting the explicit methodor the implicit method as the sounding method (step S601). In thepresent example, it is assumed that the explicit method is selected. InF1111, the AP 102 confirms the CSI processing capability of the STA 103(step S602). This is performed by referencing the STA management table.In F1112, the AP 102 selects the sounding method by the CSI processingcapability of the STA 103 (step S602).

Next, the operation sequence of the AP 102 and the STA 103 in eachsounding method selected in F1112 will be described with reference toFIG. 12 to FIG. 14 .

<Simultaneous NDP Transmission (No BFRP TF)>

FIG. 12 is a sequence in which the CSI processing capability of the STA103 is determined to be “high” (“high” in step S602) and the soundingmethod that is selected in F1112 in FIG. 11 is “a case of a simultaneousNDP transmission (No BFRP TF)” (step S603). In F1201, a sounding TF istransmitted to the AP 105 from the AP 102. This sounding TF is a framethat is used by the Master-AP and the Slave-AP for simultaneouslytransmitting a NDP. A sounding TF is transmitted to the Slave-AP fromthe Master-AP. This sounding TF does not exist in the IEEE 802.11axstandard but can be achieved by a frame of the same format as theTrigger Frame 800 in FIG. 8 . In such a case, the value of the TriggerType 811 is any one of “8” to “15” that is reserved. In F1202, the AP102 transmits an NDPA (NDP Announcement) to the STA 103. This NDPAincludes an STA Info List of terminals that are to receive an NDP. Thisindividual STA Info List is configured by a 12-bit format Association ID(AID 12) and a Feedback Type that indicates whether the user is an SU(Single User) or an MU (Multi User), and an Nc Index. In F1203, the AP105 transmits the NDPA to the STA 103. Here, F1202 and F1203 areperformed after the SIFS has elapsed from F1201. In F1204, the AP 102transmits an NDP to the STA 103. In F1205, the AP 105 transmits an NDPto the STA 103. Here, F1204 and F1205 are performed after the SIFS haselapsed from F1202 (F1203).

In F1206, the CSI calculation unit 314 of the STA 103 calculates theCSI. In F1207, the STA 103 transmits a frame including a CSI reportfield 900 in FIG. 9 to the AP 102. In F1208, the AP 102 performs sharingof the CSI to and from the AP 105. Note that, this sharing may beperformed when sharing data for the STA 103 between the AP 102 and theAP 105 or immediately prior to a transmission of data to the STA 103.Note that a configuration may be taken so as to perform the transmissionin F1202 without performing the transmission in F1201 or F1203. In sucha case, the AP 105 can control an address and a timing for the NDPtransmission in F1205 in accordance with the content of a sounding TF inF1201 from the AP 102.

<Simultaneous NDP Transmission (No BFRP TF)>

FIG. 13 is a sequence in which the CSI processing capability of the STA103 is determined to be “medium” (“medium” in step S602) and thesounding method that is selected in F1112 in FIG. 11 is “a case of asimultaneous NDP transmission (with BFRP TF)” (step S604, step S605).The processing from F1201 to F1205 are the same as in the case of“simultaneous NDP transmission (no BFRP TF)” in FIG. 12 .

The difference from FIG. 12 is that the AP 102 transmits a BFRP TF(BeamForming Report Poll Trigger Frame) to the STA 103 in F1301. ThisBFRP TF can be achieved by a frame of the same format as the TriggerFrame 800 in FIG. 8 . In such a case, the value of the Trigger Type 811is “7”. Further, the AP 102 decides a padding for CSI (step S604). Asdescribed above, the AP 102 decides the padding time for CSI so that thelarger the CSI processing capability is in relation to the CSIprocessing capability that is classified in the same “medium” level, theshorter the padding time for CSI. Note that this means that the numberof bits of the padding 807 in FIG. 8 will further increase. The padding807 is data whose bit sequence is all 1. The STA (terminal) that isanalyzing the structure of the trigger frame indicated in FIG. 8 candetermine that the Per User Info 806 is ended in accordance with thedata whose bit sequence is all 1. This determination is by the IEEE802.11ax standard.

Further, the STA can allocate the calculation resource of the controlunit 202 to another processing from the analysis of the trigger frame bythis end determination. Note that the CSI calculation by the STA 103 inF1302 in FIG. 13 starting in the middle of a padding for CSI is aschematic representation of that. Here, in this sequence diagram, timeelapses in a direction from the top to the bottom. Also, the length ofF1302 in a longitudinal direction being longer than the length of F1206in a longitudinal direction indicates that the CSI calculationcapability in the STA 103 is lower.

By such a configuration of the BFRP TF, the STA 103 in F1207 can performa CSI transmission after the SIFS elapses from the end of the padding807 including a padding for CSI. The processing in F1208 is the same asin a case of “simultaneous NDP transmission (no BFRP TF)” in FIG. 12 .

Note that in FIG. 13 , the STA 103 starts a CSI calculation in F1302after receiving the BFRP TF in F1301. The flow of this processing is anexample and a configuration may be taken such that the STA 103 starts aCSI calculation after receiving an NDP in F1204 and F1205, temporarilyinterrupt the calculation during the reception of BFRP TF in F1301, andthen resume the calculation after determining that the Per User Info 806is ended.

<Sequential NDP Transmission>

FIG. 14 is a sequence in which the CSI processing capability of the STA103 is determined to be “low” (“low” in step S602) and the soundingmethod that is selected in F1112 in FIG. 11 is “a case of a sequentialNDP transmission” (step S606). The processing in F1201 is the same as ina case of “simultaneous NDP transmission (no BFRP TF)” in FIG. 12 . InF1401, the AP 102 transmits an NDPA (NDP Announcement) to the STA 103.In F1402, the AP 105 transmits the NDPA to the STA 103. In F1403, the AP102 transmits the NDPA to the STA 103. In F1404, the STA 103 calculatesand then holds the CSI. In F1405, the AP 105 transmits an NDP to the STA103. As described above, “in a case of a sequential NDP transmission”,the AP 102 (Master-AP) and the AP 105 (Slave-AP) transmit an NDP to theSTA 103 at their respective timings (F1403, F1405).

In F1406, the STA 103 calculates and then holds the CSI. In F1407, theAP 102 transmits the BFRP TF of the STA 103. In this BFRP TF, thepadding for CSI that is included in the BFRP TF that is transmitted bythe AP 102 in F1301 in FIG. 13 is not added. The reason is that it isassumed that in the STA 103, a CSI calculation that is related to oneNDP is possible within the SIFS time. The processing from F1207 andF1208 are the same as in the case of “simultaneous NDP transmission (noBFRP TF)” in FIG. 12 .

Note that the above embodiment is something to be applied in allmulti-AP coordination configurations; however, a configuration may betaken so as to limit the use case to a case of null steering or a JTX(Joint Transmission) that uses a D-MIMO (Distributed Multiple InputMultiple Output).

Also, in any of the cases in FIG. 12 to FIG. 14 , data transmission tothe STA 103 is performed by control of the AP 102 after the AP 102 andthe AP 105 have received the CSI report (step S608).

As described above, each AP can obtain the CSI from the STA at a desiredtiming without reducing the amount of information by performing thesounding processing by a method decided in accordance with the CSIprocessing capability of the STA. By this, it becomes possible toachieve high-speed/high-efficiency/stable wireless communication by themulti-AP coordination configuration. Also, by executing sounding withoutreducing the CSI, it becomes possible to achieve improvement in usageefficiency of a wireless medium and system-wide and individualcommunication speed and stability which are the aims of the IEEE802.11bestandard.

Other Embodiments

Embodiment(s) of the present invention can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2020-002435, filed Jan. 9, 2020, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A communication apparatus operable to act as amaster-AP (access point) in a multi-AP coordination configuration thatsupports an IEEE802.11 series standard, the communication apparatuscomprising: a selection unit configured to select a sounding methodwhich is a method for transmitting a sounding packet for receiving a CSI(channel state information) report as feedback from a terminal apparatusin accordance with a CSI calculation capability in the terminalapparatus that is connected to the communication apparatus, wherein theCSI calculation capability is indicated by two or more valuesrepresenting two or more levels of calculation capability, and whereinthe selection unit selects a first sounding method in a case where theCSI calculation capability indicates a first level and a second soundingmethod in a case where the CSI calculation capability indicates a secondlevel representing a calculation capability lower than the first level.2. The communication apparatus according to claim 1, further comprising:a reception unit configured to receive a predetermined frame from theterminal apparatus, wherein in a case where a value indicating a CSIcalculation capability is included in the predetermined frame, theselection unit selects the sounding method based on a received valueindicating the CSI calculation capability.
 3. The communicationapparatus according to claim 2, wherein the value indicating the CSIcalculation capability is indicated by a capabilities element within aninformation element in the predetermined frame.
 4. The communicationapparatus according to claim 2, further comprising: a setting unitconfigured to set the value indicating the CSI calculation capabilitybased on a value of a trigger frame MAC padding duration in a case wherethe value indicating the CSI calculation capability is not included andthe trigger frame MAC padding duration is included in the predeterminedframe, wherein the selection unit selects the sounding method based onthe set value indicating the CSI calculation capability.
 5. Thecommunication apparatus according to claim 2, further comprising: asetting unit configured to set a value indicating the CSI calculationcapability based on a default value in a case where the value indicatingthe CSI calculation capability is not included and a trigger frame MACpadding duration is included in the predetermined frame, wherein theselection unit selects the sounding method based on the set valueindicating the CSI calculation capability.
 6. The communicationapparatus according to claim 2, wherein the predetermined frame is oneof a beacon, a probe request/response, an association request/response,and an authentication request/response frame.
 7. The communicationapparatus according to claim 1, wherein the first level indicates “high”and the second level indicates “low”, and in a case where the selectionunit selects a third sounding method in a case where the CSI calculationcapability indicates a third level different from the first and secondlevels and indicates “medium”.
 8. The communication apparatus accordingto claim 7, wherein the first sounding method is a method in which thecommunication apparatus and a slave-AP in the multi-AP coordinationconfiguration simultaneously transmit a null data packet (NDP) as asounding packet, the third sounding method is a method in which thecommunication apparatus transmits a BFRP TF (beamforming report polltrigger frame) after the communication apparatus and the slave-AP havesimultaneously transmitted the NDP, and the second sounding method is amethod in which the communication apparatus and the slave-AP transmitthe NDP at separate timings.
 9. The communication apparatus according toclaim 8, wherein in the BFRP TF that is transmitted in the secondsounding method, a padding having a length based on the value indicatingthe CSI calculation capability is included.
 10. The communicationapparatus according to claim 1, wherein the first level indicates “high”and the second level indicates “low”.
 11. The communication apparatusaccording to claim 10, wherein the first sounding method is a method inwhich a slave-AP in the communication apparatus and the multi-APcoordination configuration simultaneously transmit a null data packet(NDP) as a sounding packet and the second sounding method is a method inwhich the communication apparatus and the slave-AP transmit the NDP atseparate timings.
 12. A method of controlling a communication apparatusoperable to act as a master-AP (access point) in a multi-AP coordinationconfiguration that supports an IEEE802.11 series standard, the methodcomprising: selecting a sounding method which is a method fortransmitting a sounding packet for receiving a CSI (channel stateinformation) report as feedback from a terminal apparatus in accordancewith a CSI calculation capability in the terminal apparatus thatconnected to the communication apparatus, wherein the CSI calculationcapability is indicated by two or more values representing two or morelevels of calculation capability, and wherein a first sounding method isselected in a case where the CSI calculation capability indicates afirst level and a second sounding method is selected in a case where theCSI calculation capability indicates a second level representing acalculation capability lower than the first level.
 13. A non-transitorycomputer-readable storage medium storing a computer program for causinga computer to execute a method for controlling a communication apparatusacting as a master-AP (access point) in a multi-AP coordinationconfiguration that supports an IEEE802.11 series standard, the methodcomprising: selecting a sounding method which is a method fortransmitting a sounding packet for receiving a CSI (channel stateinformation) report as feedback from a terminal apparatus in accordancewith a CSI calculation capability in the terminal apparatus thatconnected to the communication apparatus, wherein the CSI calculationcapability is indicated by two or more values representing two or morelevels of calculation capability, and wherein a first sounding method isselected in a case where the CSI calculation capability indicates afirst level and a second sounding method is selected in a case where theCSI calculation capability indicates a second level representing acalculation capability lower than the first level.
 14. The communicationapparatus according to claim 1, wherein the second sounding method is amethod in which the communication apparatus and a slave-AP in themulti-AP coordination configuration simultaneously transmit a null datapacket (NDP) as a sounding packet and then transmits a BFRP TF(beamforming report poll trigger frame) at least after, the firstsounding method is a method in which the communication apparatus and theslave-AP simultaneously transmit the null data packet as a soundingpacket and then receive a response of the NDP without transmitting theBFRP TF.
 15. A communication apparatus operable to act as a master-AP(access point) in a multi-AP coordination configuration that supports anIEEE802.11 series standard, the apparatus comprising: a selection unitconfigured to select a sounding method which is a method fortransmitting a sounding packet for receiving a CSI (channel stateinformation) report as feedback from a terminal apparatus in accordancewith a CSI calculation capability in the terminal apparatus that isconnected to the communication apparatus, wherein the CSI calculationcapability is three or more values, and wherein the selection unitselects a first sounding method in a case where the CSI calculationcapability indicates a first level and a second sounding method in acase where the CSI calculation capability indicates a second levelrepresenting a calculation capability lower than the first level and athird sounding method in a case where the CSI calculation capabilityindicates a third level representing a calculation capability lower thanthe second level.